1. Field
The present embodiments relate to an organic light-emitting device and a method of manufacturing the same.
2. Description of the Related Technology
In an organic light-emitting device including an anode, a cathode, and an organic layer between the anode and cathode, a mixture of magnesium (Mg) and silver (Ag) is currently being widely used to manufacture the cathode, particularly, of a top-emission light-emitting device.
Magnesium, having a low-work function and which is good to form a thin film on an electron injection layer (EIL), is advantageous in terms of electron injection and device stability. Ag has good reflection characteristics, and may form micro-cavities along with a reflective anode when used to form the cathode, thereby improving efficiency of a device.
However, a cathode made of Mg and Ag has a very high resistance, and thus is not suitable to implement uniform-quality images on a front panel, and additional compensation circuits are required in this regard.
Even when a capping layer (CPL) consisting of an organic material or an oxide having a high refractive index is further deposited on the cathode made of Mg and Ag, light generated in the organic light-emitting device may have low transmittance. Furthermore, the Mg—Ag cathode with such a thin film absorbs a larger amount of light than thin-film type cathodes consisting of other metals, and thus may reduce the efficiency of the organic light-emitting device.
To address these drawbacks, thin-film cathodes in various composition ratios of Mg and Ag have been suggested. The higher the percentage of Ag, the lower the light absorption by the thin-film type cathode, the higher the light reflection, and the better the resistance characteristics. However, the higher percentage of Ag may hinder the injection of electrons and lead to a higher driving voltage and a lower efficiency of the organic light-emitting device. Also, the higher the percentage of Mg, the higher the light absorption due to Mg, the lower the efficiency of the organic light-emitting device, and the higher the resistance.
In order to improve the resistance and transmittance characteristics of conventional Mg—Ag thin-film type cathodes, a top-emission organic light-emitting device including a thin film cathode consisting of only Ag has been suggested. In this regard, a capping region of the top-emission organic light-emitting device defined for improving external emission efficiency consists of oxide alone, and materials for an electron injection layer are limited to LIF/Al, Mg, Ag, ytterbium (Yb), rubidium (Rb), cesium (Cs), barium (Ba), calcium (Ca)-aluminum (Al), Mg—Al, Li/Al, Li2O/Al, and mixtures thereof. However, considering the nature of oxide, high-temperature deposition or sputtering is necessary for such organic light-emitting devices, which may damage the thin film Ag cathode and may limit materials available for the electron injection layer.
Therefore, there is a demand for an organic light-emitting device structure providing good optical characteristics at a reasonable resistance and which facilitates injection of electrons.